For diabetics, it is important to know their own glucose levels and it is necessary to decide the timing of insulin administration by repetitively measuring the glucose levels. For example, the glucose level measurement is performed using a disposable glucose sensor (See Patent Document 1: JP-B-H08-10208, for example). To measure the glucose level using the glucose sensor disclosed in the document, blood need be extracted from the skin using a lancing apparatus. Therefore, the monitoring of the glucose level is troublesome for diabetics, and the necessity of sticking a needle into the skin at each time of glucose level measurement causes pain.
To solve such problems, a technique to continuously monitor the glucose level has been proposed (See Patent Document 2: JP-A-H09-503924, for example), which has been commercialized as “Gluco Watch” in the United States. The glucose level measuring technique employs an electrode method in which blood or interstitial fluid extracted from the skin is supplied to an electrode to measure the glucose level by using the electrode. The electrode in this case is arranged in close proximity to the skin in measuring the glucose level and is designed so that an electron taken from the blood or interstitial fluid via glucose oxidase (hereinafter, sometimes simply referred to as “GOD” is supplied to the electrode (conductive component).
The electrode method using GOD has a drawback that the accuracy of measurement may be deteriorated by the influence of dissolved oxygen in the sample (blood or interstitial fluid). Generally, in the method using GOD, the supply of the electron, which GOD took from glucose, to the electrode (conductive component) is performed by either of the following two methods: in one of the methods, hydrogen peroxide is generated so that the electron is supplied to the electrode (conductive component) via hydrogen peroxide, whereas, in the other method, the electron is supplied to the electrode (conductive component) via an electron mediator (e.g. metal complex such as potassium ferricyanide). Both of the methods hardly cause problems to the human body as long as the measurement of the glucose level using blood or the like extracted from the skin is performed at a place separated from the skin. However, considering that hydrogen peroxide and potassium ferricyanide are the substances which are not good for the human body, the method in which the electrode containing GOD is disposed in close proximity to the skin, like the forgoing method, is not preferable.
Further, in the method which utilizes an electron mediator, it is necessary to add an electron mediator into the electrode or mobilize an electron mediator at the electrode surface. In both cases, the preparation of an electron mediator separately from GOD and adding the electron mediator to the electrode is disadvantageous in terms of cost.
Patent Document 1: JP-B-H08-10208
Patent Document 2: JP-A-H09-503924